"Please look at this porcelain skin. I'm like a human sink."
Why it's apropos: What are three things Sheldon seems to have in common with a porcelain sink? They're both silky, shiny, and sans pores.
What's the biggest difference, though? Sheldon would never let anyone put their dirty paws on his basin.
"The Celebration Experimentation" (Episode 17, Season 9)